Pre-distortion is used to compensate for the non-linearity of a power amplifier in order to reduce the non-linearity effects in an amplified signal. Pre-distortion may be improved by reducing the electrical memory of the power amplifier.
Known techniques attempt to minimize electrical memory by reducing the common mode impedance at the drain or collector of the transistor of a power amplifier. According to one known technique, a first wire is attached between the output terminals of the transistor to form a differential mode inductor. A second wire is attached to the center point of the first wire to form a common mode point to bring in a DC bias voltage. This known technique, however, does not achieve satisfactory reduction of common mode impedance in certain situations. According to another known technique, a conventional autotransformer may be wound on a toroidal core. The center tap of the autotransformer forms the common mode point for the DC bias circuitry, and the remaining two leads form the differential mode inductor. This known technique, however, is not suitable in certain situations.
It is generally desirable to have satisfactory reduction of common mode impedance in certain situations.